1. Field of the Invention
The present invention relates to a molding machine equipped with a drive unit for linearly moving a movable body, such as a movable platen of a clamping apparatus.
2. Description of the Relevant Art
A clamping apparatus (molding machine) equipped with a drive unit employing a linear motor for reciprocating a movable platen which supports a movable mold is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 61 (1986)-154822. The disclosed clamping apparatus employs a linear motor and an electromagnet. The linear motor is adapted to reciprocate the movable platen in order to open/close a mold. The electromagnet is adapted to apply high pressure to the mold for clamping purpose.
However, such a clamping apparatus involves the following problems.
First, since clamping is effected by the electromagnet, a clamping pressure cannot be controlled with a high degree of accuracy. Because of poor controllability, a series of clamping operation cannot be controlled precisely and smoothly.
Second, since the drive unit employs mutually independent commercial linear motor and electromagnet, the number of components increases. As a result, the overall structure of a molding machine becomes complicated and increases in size, resulting in an increase in overall cost.